Luibar
These questions have been asked and answered many times.
yes one can
C class will be allocated with ANA as priority but it is available on other operations, if the requirements set by the company are met, I do not believe the contractor is in a position to select.
I suggest you have a good read at the thread, especially the most recent few pages, it may answer a lot of questions you may not have considered yet. This job is not for everyone and it is very important to do your homework thoroughly before jumping in.